[Insert Fig. 8 here]
4 Discussion
4.1 DRM vs. other heat-pulse based methods
The double-ratio method (DRM) presented here was more robust than other common heat pulse methods (HRM, CHPM and Tmax) across a wide range of sap velocity, in both theoretical and experimental tests. In theoretical tests, the DRM produced the least bias and smallest variance among the four methods. In experimental tests, the DRM accurately tracked diel trends in tree water use (as measured by lysimetry) from 0-7 kg h-1 or 0-100 cm h-1.
The applicable upper limit for the HRM can be roughly estimated from Eqn. 4 , given the resolution of temperature sensors and peak rise in temperature. For example, if we assume:
then with a probe spacing of 1.5 cm and k = 0.0025 cm2 s-1, the upper limit of velocity that the HRM can estimate is,